1. Field of the Invention
The present invention relates to a two-dimensional (2D) /three-dimensional (3D) switchable display device, and more particularly, to a display device, which can reduce the loss of light during a process of switching a 2D display device to a 3D display device.
2. Description of the Related Art
In recent years, 3D display devices have been applied in various fields, such as medical imaging, games, advertisements, education, and military affairs. Also, many studies have been undertaken to display 3D images using holographic and stereoscopic techniques.
The holographic technique is an ideal technique, but a coherent light source is required and it is difficult to record and reproduce a large-sized object located at a long distance.
On the other hand, the stereoscopic technique employs a stereoscopic effect caused by a binocular parallax between two 2-dimensional images that are respectively seen by the two eyes of a user. Since the stereoscopic technique is performed using two planar images, 3D images with high resolution and great depth impression may be displayed in a simple manner. Stereoscopic techniques may be classified into those that use glasses which utilize polarized light and a shutter to allow two eyes to see separate images, and glassesless, autostereoscopic display in which a display device directly separates images to form fields of view. In the case of an autostereoscopic-type display device, the number of viewers is restricted because an observation range is fixed. Nevertheless, the autostereoscopic-type display device is generally preferred to a display device that requires viewers to wear additional glasses. Also, autostereoscopic-type display devices are lately showing a tendency to adopt a parallax barrier that is used to virtually create 3D images using stereo images. The parallax barrier includes vertical or horizontal slits formed in front of images corresponding to the left and right eyes and allows synthetic 3D images to be separately observed through the slits to obtain a stereoscopic effect.
FIG. 1 is a schematic construction diagram of a related art parallax-barrier-type 3D display device.
Referring to FIG. 1, left-eye pixels L for displaying image information for the left eye and right-eye pixels R for displaying image information for the right eye are alternately formed on a liquid crystal (LC) panel 10. A backlight 20 is located under the LC panel 10. The backlight 20 functions to emit light toward the LC panel 10 using electric energy. A parallax barrier 30, which is interposed between the LC panel 10 and an observer 40, allows light to pass therethrough or cuts off the light. Specifically, the parallax barrier 30 includes slits 32 through which light emitted by the right-eye pixel R and the left-eye pixel L pass and barriers 34 which cut off the light, so that the observer 40 can see virtual 3D images. As can be seen from a magnified view of the parallax barrier 30, the slits 32 and the barriers 34 are alternately formed in a vertical direction.
The above-described parallax-barrier-type 3D display device creates 3D images in the following process. Initially, light L2 of light emitted by the backlight 20 becomes light L1 passes through the left-eye pixel L of the LC panel 10 and the slit 32 of the parallax barrier 30 and reaches the left eye of the observer 40. However, although light L2 of light emitted by the backlight 20 passes through the left-eye pixel L of the LC panel 10, since the light L2 travels toward the right eye of the observer 40, the light L2 is cut off by the barrier 34 and cannot reach the observer 40. Likewise, light R1 of light emitted by the backlight 20 passes through the right-eye pixel R of the LC panel 10 and the slit 32 of the parallax barrier 30 and reaches the right eye of the observer 40. However, although light R2 of light emitted by the backlight 20 passes through the right-eye pixel R of the LC panel 10, since the light R2 travels toward the left eye of the observer 40, the light R2 is cut off by the barrier 34 and cannot reach the observer 40. As a result, light that passes through the left-eye pixel L corresponds to the light L1 that is transmitted only to the left eye of the observer 40, while light that passes through the right-eye pixel R corresponds to the light R1 that is transmitted only to the right eye of the observer 40, so that the observer 40 can recognize the light L1 and R1. In this case, sufficient parallax information is provided between the light L1 and the light R1 so that the observer 40, which is a human being, can appreciate 3D images.
A 2D/3D switchable display device has been introduced by putting a 3D display device to practical use in order to relieve fatigue caused by optical illusions between both eyes. The 2D/3D switchable display device may be embodied by forming the parallax barrier 30 of FIG. 1 using liquid crystals (LCs). Specifically, when power is supplied to the LCs, some pixels function as the barriers 34 that cut off/absorb light emitted by the backlight 20, and the other pixels to which no power is supplied function as the slits 32 of the parallax barrier 30 to create 3D images. Also, when no power is supplied to the LCs, the parallax barrier 30 is not formed so that the same image is transmitted to the right and left eyes of the observer 40 to display 2D images.
When 3D images are displayed, a lot of light is cut off and absorbed by the barriers 34, thus lowering optical efficiency. Owing to low optical efficiency, it is difficult to minimize the size of the slits 32 to lessen crosstalk in a 3D mode. Also, as the number of viewpoints increase, the portion of pixels that are screened by barriers increases. Accordingly, optical efficiency further deteriorates, thus precluding the use of the parallax-barrier-type 3D display device in a multi-mode.
FIG. 2 is a construction diagram of a related art parallax-barrier-type 3D display device in which a reflection layer is formed on barriers, which is proposed in order to improve optical efficiency.
Referring to FIG. 2, an aluminum coating layer 66 is formed on barriers 63 in which light emitted by a backlight 60 is absorbed, so that light is sent back to a reflection plate 69 and recycled. The structure shown in FIG. 2 may be applied to a 3D display device, but not to a 2D/3D switchable display device.